Shiva hypothesis
William Napier and Victor Clube published a paper in the journal Nature during 1979. Their article carried the title A Theory of Terrestrial Catastrophism. They argued that gravitational disturbances occur when the Solar System crosses the plane of the Milky Way galaxy. This crossing disturbs comets within the Oort cloud surrounding our star system. These disturbed comets travel toward the inner Solar System. The result is an increased chance of impact events on Earth. The hypothesis suggests these large impacts happen roughly every 30 million years. One such event marks the Cretaceous, Paleogene extinction.
The Sun moves through space relative to the center of the Milky Way galaxy. Its path takes it above and below the galactic disk repeatedly over time. When the Solar System intersects this flat plane, gravity pulls on distant objects. Comets residing in the Oort cloud feel this pull strongly. Some comets are knocked off their stable orbits. They fall inward toward the planets we know today. This mechanism creates a cycle of potential collisions. The frequency of these crossings sets the rhythm for mass extinctions. Evidence points to intervals near 30 million years between major impacts.
Michael R. Rampino began publishing follow-up research starting in 1984. His work referenced the earlier publication by Napier and Clube directly. A letter he co-wrote with Stothers appeared in Nature that same year. During the 1990s, Rampino and Bruce Haggerty renamed the theory after Shiva. This Hindu god represents destruction within ancient traditions. Their new title became known as the Shiva hypothesis. In 2020, Rampino and colleagues published non-marine evidence supporting previous marine findings. These studies aimed to corroborate claims about periodic extinction events.
Some models suggest the Sun passes through higher density spiral arms instead of crossing the galactic plane. Such passages could hypothetically coincide with mass extinction periods on Earth. However, reanalysis using CO data failed to find a correlation there. Another theory proposes a brown dwarf named Nemesis drives cycles every 26 million years. This interval varies slightly from the 30 million-year cycle proposed by Napier and Clube. Critics note these alternative explanations lack consistent observational support compared to the original proposal.
Critics argue that assuming all extinctions share one cause is flawed. Evidence suggests most extinction events result from a variety of different causes. These diverse triggers are unlikely to be cyclically induced by a single mechanism. The idea of strict periodicity faces significant challenges from geological records. Scientists point out that impacts cannot explain every major loss of biodiversity. The assumption of a universal cyclic trigger remains contested within the field.
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Common questions
What is the Shiva hypothesis and who proposed it?
The Shiva hypothesis is a scientific theory concerning impact events that suggests gravitational disturbances occur when the Solar System crosses the plane of the Milky Way galaxy. William Napier and Victor Clube published this paper in the journal Nature during 1979 under the title A Theory of Terrestrial Catastrophism.
How often does the Shiva hypothesis suggest large impacts happen on Earth?
The hypothesis suggests these large impacts happen roughly every 30 million years. Evidence points to intervals near 30 million years between major impacts, with one such event marking the Cretaceous Paleogene extinction.
When did Michael Rampino rename the theory after Shiva?
During the 1990s, Rampino and Bruce Haggerty renamed the theory after Shiva. This Hindu god represents destruction within ancient traditions and their new title became known as the Shiva hypothesis.
Why do critics argue against the periodicity of the Shiva hypothesis?
Critics argue that assuming all extinctions share one cause is flawed because evidence suggests most extinction events result from a variety of different causes. These diverse triggers are unlikely to be cyclically induced by a single mechanism according to geological records.
What alternative theories exist regarding mass extinction cycles besides the Shiva hypothesis?
Some models suggest the Sun passes through higher density spiral arms instead of crossing the galactic plane while another theory proposes a brown dwarf named Nemesis drives cycles every 26 million years. Critics note these alternative explanations lack consistent observational support compared to the original proposal.